I THINK that the lockplate on your gun was made by James Golcher of Philadelphia.

My book unfortunatly has very very little information on him, only listing him as being in Philadelphia in 1855/1861. It doesn't give a reference for that information (such as tax lists, business directories, etc.)

And, that information doesn't seem to square with an illustration earlier in the book showing a Golcher lock in an early 1800s flint style.

Your friend may want to write to or contact the Philadelphia Historical Society, or the Pennsylvania State Museum & Historial Commission for more information.